1. Field of the Invention
The present invention generally relates to a wireless communication method, a wireless communication system and a wireless communication device.
Priority is claimed on Japanese Patent Application No. 2005-088198, filed Mar. 25, 2005, the contents of which are incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
A conventional mobile communication system includes a base station and one or more mobile stations such as mobile terminals. The base station has an array antenna that includes a plurality of antenna elements that have a directional pattern for transmitting and receiving radio waves. The array antenna follows movement of the mobile station. In view of maintaining a desired quality of wireless communication between the base station and the mobile station, it is preferable for the mobile terminal such as a mobile telephone to have an array antenna with a directional pattern for transmitting and receiving radio waves so as to improve an ability to continue wireless communication access to the base station.
Typical examples of the known methods of controlling the directivity of the array antenna may include, but are not limited to, adaptive algorithms such as an RLS algorithm, an SMI algorithm, an LMS algorithm, all of which refer to Minimum Mean-Squared Error (MMSE). The mobile station uses the adaptive algorithm to calculate a weight factor of each of the antenna elements that form the directional pattern of the array antenna, wherein the calculation is made so as to minimize a squared error of a received signal from the base station with reference to a reference signal, thereby directing a null point toward an arrival point of an interference wave and also directing a main beam toward another arrival point of a desired wave. This technique is disclosed by KIKUMA Nobuyoshi in “Adaptive Signal Processing with Array Antenna” published November 1998 by Kagaku Gijyutsu Publishing Co., Ltd.
The adaptive array system is one of the typical wireless communication techniques using array antennas. Another example of the wireless communication techniques using array antennas is a multi-input multi-output (MIMO). In the multi-input multi-output (MIMO) system, each of the base station and the mobile station has an array antenna that includes a plurality of antenna elements. A plurality of propagation paths for a spatial division multiple access are established between a first plurality of antenna elements of the base station and a second plurality of antenna elements of the mobile station. The spatial division multiple access improves the communication speed. When each of the mobile station and the base station has an array antenna including four antenna elements, four propagation paths for the spatial division multiple access are established between a single pair of the mobile station and the base station. The spatial division multiple access through the four propagation paths provides an increased communication speed which is four-fold higher than the communication speed provided by using a single propagation path between the base station and the mobile station.
The adaptive array system and the multi-input multi-output (MIMO) system are different from each other in the adaptivity of a wireless propagation path. A suitable one of the adaptive array system and the multi-input multi-output (MIMO) system is selected in accordance with the current state of the wireless propagation path. When each of the base station and the mobile station has the array antenna including the plurality of the antenna elements, a plurality of propagation paths are established between a plurality of combinations of the antenna elements of the base station and the mobile station. When a spatial orthogonality of the wireless communication channels is higher than a predetermined threshold level, the propagation paths are highly suitable and adaptable to the multi-input multi-output (MIMO) system. When a spatial orthogonality of the wireless communication channels is lower than a predetermined threshold level, the propagation paths are highly suitable and adaptable to the adaptive array system.
In the communication system, the change in the state of propagation of radio waves between a transmitter station and a receiver station is continuous. The continuous change causes a continuous change in the spatial orthogonality between the propagation paths that are established between the plural combinations of the antenna elements of the base station and the mobile station. It is desired to continue monitoring the spatial orthogonality and select a more suitable one of the adaptive array system and the multi-input multi-output (MIMO) system. The adaptive array system and the multi-input multi-output (MIMO) system are different from each other in a process of adding a signal to the antenna element. It is difficult for the conventional techniques to switch between the adaptive array system and the multi-input multi-output (MIMO) system without discontinuing the current communication. When the adaptive array system is switched to the multi-input multi-output (MIMO) system, it is preferable to estimate the spatial orthogonality between the wireless propagation paths that are established between the plural combinations of the antenna elements of the base station and the mobile station. It is difficult for the conventional technique to estimate the spatial orthogonality without discontinuing the current communication between the base station and the mobile station.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved system, method and/or apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.